Ioannis Kontogiannis

Leibniz Institute for Astrophysics Potsdam

Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the...

Vortex flows, related to solar convective turbulent dynamics at granular scales and their interplay with magnetic fields within intergranular lanes, occur abundantly on the solar surface and in the atmosphere above. Their presence is revealed in high-resolution and high-cadence solar observations from the ground and from space and with state-of-the...

Solar flares and coronal mass ejections (CMEs) cause immediate and adverse effects on the interplanetary space and geospace. The deeper understanding of the mechanisms that produce them and the construction of efficient prediction schemes are of paramount importance. The source regions of flares and CMEs exhibit some common morphological characteri...

Solar flares and coronal mass ejections (CMEs) cause immediate and adverse effects on the interplanetary space and geospace. In an era of space-based technical civilization, the deeper understanding of the mechanisms that produce them and the construction of efficient prediction schemes are of paramount importance. The source regions of flares and...

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operatin...

Context. Chromospheric swirls are related to convectively driven vortex flows and considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties. Aims. We aim to detect and track chromospheric swirls...

Chromospheric swirls are considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties. We applied a recently developed automated chromospheric swirl detection method to time-series observations of a...

Aims. In this work, we explore the spectral window containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g -factors between 1.6 and 2.5. The goal is to simultaneously analyze 15 spectral lines, comprising Cr I , Cu I , Fe I , Mn I , and S...

The spectral window, containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 \r{A}, with Land\'e g-factors between 1.6 and 2.5, is explored. The goal is to analyze simultaneously 15 spectral lines, which comprise Cr I, Cu I, Fe I, Mn I, and Si I lines, w...

The European Union funded the FLARECAST project, that ran from January 2015 until February 2018. FLARECAST had a research-to-operations (R2O) focus, and accordingly introduced several innovations into the discipline of solar flare forecasting. FLARECAST innovations were: first, the treatment of hundreds of physical properties viewed as promising fl...

The EU funded the FLARECAST project, that ran from Jan 2015 until Feb 2018. FLARECAST had a R2O focus, and introduced several innovations into the discipline of solar flare forecasting. FLARECAST innovations were: first, the treatment of hundreds of physical properties viewed as promising flare predictors on equal footing, extending multiple previo...

The H{\alpha} spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in H{\alpha} include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mott...

We analyse the temporal evolution of the Differential Emission Measure (DEM) of solar active regions and explore its usage in solar flare prediction. The DEM maps are provided by the Gaussian Atmospheric Imaging Assembly (GAIA-DEM) archive, calculated assuming a Gaussian dependence of the DEM on the logarithmic temperature. We analyse time-series o...

Context. Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it. Aims. We investigate the nature and characteristics of waves within this quiet-Sun vortex flow, over the course of an uninterrupted...

Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it. We investigate the nature and characteristics of waves within this quiet-Sun vortex flow to better understand its physics and dynamics. We u...

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument s...

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument s...

Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument s...

Aims. Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and H α l...

Aims. To investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere, observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and H-alpha lines wi...

We study the evolution of a mini-filament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high-spectral resolution imaging spectroscopy in H$\alpha$ acquired by the echelle spectrograph of the Vacuum Tower Telescope (VTT), Tenerife, Spain, photospheric magnetic field observations from the...

A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (HOP~338, 20\,--\,30~September 2017), the GREGOR solar telescope, and the \textit{Vacuum Tower Telescope} (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole region t...

Aims. The regular pattern of quiet-Sun magnetic fields was disturbed by newly emerging magnetic flux, which led a day later to two homologous surges after renewed flux emergence, affecting all atmospheric layers. Hence, simultaneous observations in different atmospheric heights are needed to understand the interaction of rising flux tubes with the...

A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (Hinode Observing Plan 338, 20 – 30 September 2017), the GREGOR solar telescope, and the Vacuum Tower Telescope (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole re...

High-spectral resolution observations using the VTT echelle spectrograph in the chromospheric H$\alpha$ line were obtained in the early growth phase of active region NOAA 12722. Noise-stripped H$\alpha$ line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. The SDO...

Context. We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence in the photosphere to its appearance in the corona and its decay. Aims. We track processes and phenomena that take place across all atmospheric layers; we explore their interrelations and compare our findings with those from recent numer...

We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence to its decay. We track processes and phenomena across all atmospheric layers, explore their interrelations and compare our findings with recent numerical modelling studies. We used imaging, spectral and spectropolarimetric observations from space...

The effective connected magnetic field strength (Beff) is a useful proxy which has been successfully implemented as a predictor of the solar flare occurrence in the past (e.g. A-Effort, FORSPEF, FLARECAST). In the current work, the line-of-sight (LOS) Beff values for each active region (AR) of the period 09/2012-12/2018 were calculated using SHARP...

We investigate the relation between characteristics of coronal mass ejections and parameterizations of the eruptive capability of solar active regions widely used in solar flare-prediction schemes. These parameters, some of which are explored for the first time, are properties related to topological features, namely, magnetic polarity-inversion lin...

We investigate the relation between characteristics of coronal mass ejections and parameterizations of the eruptive capability of solar active regions widely used in solar flare prediction schemes. These parameters, some of which are explored for the first time, are properties related to topological features, namely, magnetic polarity inversion lin...

We study the evolution of the decaying active region NOAA 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph (GRIS), spectral imaging time-series in the Na I D ² spectral...

The Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide...

Context . Recently, the appearance, characteristics, and dynamics of a persistent 1.7 h vortex flow, resembling a small-scale tornado, have been investigated with observations both from the ground and from space in a quiet-Sun region in several lines and channels and for the first time in the H α line centre. The vortex flow showed significant subs...

Context . Vortex flows have been extensively observed over a wide range of spatial and temporal scales in different spectral lines, and thus layers of the solar atmosphere, and have been widely found in numerical simulations. However, signatures of vortex flows have only recently been reported in the wings of the H α , but never so far in the H α l...

Efficient prediction of solar flares relies on parameters that quantify the eruptive capability of solar active regions. Several such quantitative predictors have been proposed in the literature, inferred mostly from photospheric magnetograms and/or white-light observations. Two of them are the Ising energy and the sum of the total horizontal magne...

We investigate the morphology and temporal variability of a quiet Sun network region in different solar layers. The emission in several EUV spectral lines through both raster and slot time series, recorded by EIS/Hinode is studied along with H$\alpha$ observations and high resolution spectropolarimetric observations of the photospheric magnetic fie...

We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the S...

The effect of using two representations of the normal-to-surface magnetic field to calculate photospheric measures that are related to active region (AR) potential for flaring is presented. Several AR properties were computed using line-of-sight ($B_{\rm los}$) and spherical-radial ($B_{r}$) magnetograms from the Space-weather HMI Active Region Pat...

We explore the association of non-neutralized currents with solar flare occurrence in a sizable sample of observations, aiming to show the potential of such currents in solar flare prediction. We use the regularly produced high quality vector magnetograms by the Helioseismic Magnetic Imager and more specifically the Space weather HMI Active Region...

Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork re...

Aims. We seek indications or evidence of transmission/conversion of magnetoacoustic waves at the magnetic canopy, as a result of its impact on the properties of the wave field of the photosphere and chromosphere. Methods. We use cross-wavelet analysis to measure phase differences between intensity and Doppler signal oscillations in the Halpha, CaII...

The PROTEAS project has been initiated at the Institute of Astronomy Astrophysics, Space Applications and Remote Sensing (IAASARS) of the National Observatory of Athens (NOA). Its main objective is to provide observations, processed data and space weather nowcasting and forecasting products, designed to support the space weather research community...

Aims. We investigate the free magnetic energy and relative magnetic helicity injection in solar quiet regions. Methods. We use the DAVE4VM method to infer the photospheric velocity field and calculate the free magnetic energy and relative magnetic helicity injection rates in 16 quiet-Sun vector magnetograms sequences. Results. We find that there is...

A project is initiated at the IAASARS of the National Observatory of Athens (NOA). Its main objective is to develop techniques in order to provide forecasting tools in support of space environment services. The objective will be achieved through: a) the operation of a small full-disk solar telescope to conduct regular observations of the Sun in the...

Context. We present evidence for the conversion and transmission of wave modes on the magnetic flux tubes that constitute mottles and form the magnetic canopy in a quiet Sun region. Aims. Our aim is to highlight the details and the key parameters of the mechanism that produces power halos and magnetic shadows around the magnetic network observed in...

We investigate the free magnetic energy and relative magnetic helicity budgets of solar quiet regions. Using a novel non-linear force-free method requiring single solar vector magnetograms we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector magnetograms. As in a previous work on active r...

We present a novel nonlinear force-free method designed to calculate the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar region from a single photospheric/chromospheric vector magnetogram of the region. Our objective is to study the role of these quantities in solar eruptions and quiet-Sun dynamics. We apply the...

We investigate the interaction between acoustic oscillations and the fine-scale structures found at the chromospheric network boundaries that form the magnetic canopy. To this end, high precision photospheric magnetograms obtained by SOT/SP on-board the Hinode space mission and time series of high spatial-resolution filtergrams in five wavelengths...

We investigate the interaction between acoustic oscillations and the fine-scale structures found at the chromospheric network boundaries that form the magnetic canopy. We use high precision photospheric magnetograms obtained by SOT/SP on-board the Hinode satellite and time series of high spatial resolution filtergrams in five wavelengths along the...

Over the last two decades the uninterrupted, high-resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere...

The chromosphere is an inhomogeneous and highly dynamic layer of the solar atmosphere. New high resolution observations have revealed that it consists mainly of fine-scale structures which are directly related to the magnetic field. In this work we use multi-wavelength observations to study oscillatory phenomena in the quiet Sun and their relation...

We use a dataset of simultaneous image sequences obtained by Hinode/SOT with the Ca II H filter, as well as in Ha+-0.2A. SOT was looking at the SW solar limb. The high temporal and spatial resolution allows us to study the structure and dynamics of spicules seen at the different filters. Individual spicules have been selected and intensity and velo...

Aims: We explore the differences in the measurement of the magnetic field of the quiet solar photosphere provided by the Michelson Doppler Imager (MDI) onboard SoHO and the SpectroPolarimeter (SOT/SP) onboard Hinode and the ensuing implications for the extrapolated chromospheric magnetic field and the determination of the location of the magnetic c...

Aims: Our aim is to gain a better understanding of the interaction between acoustic oscillations and the small-scale magnetic fields of the Sun. To this end, we examine the oscillatory properties of a network region and their relation to the magnetic configuration of the chromosphere. We link the oscillatory properties of a network region and their...

We analyze the temporal behavior of a solar quiet region using a set of multi-wavelength observations obtained during a coordinated campaign. The observations were acquired by the ground-based Dutch Open Telescope (DOT), the Michelson Doppler Imager (MDI) on-board SOHO and the UV filters of the Transition Region and Coronal Explorer (TRACE). A larg...

Context. We investigate the oscillatory behavior of the quiet solar chromosphere and its discrete components in terms of oscillation properties, i.e. network and internetwork. For this purpose, we use a time series of high resolution filtergrams at five wavelengths along the Halpha profile, obtained by the Dutch Open Telescope. Aims: We aim to gain...

The Interactive Exhibition of Science and Technology is installed in an area of 1200 m 2 at the Eugenides Foundation. 65 interactive exhibits, designed by the “Cites des Science et de l’ Industrie” are organised in themes, stimulate the visitors’ mind and provoke scientific thinking. Parallel activities take place inside the exhibition, such...

We use a dataset of simultaneous image sequences obtained by Hinode/SOT with the Ca II H filter, as well as in Halpha ±0.2 ˚. SOT was looking at the SW solar limb. The high temporal A and spatial resolution allows us to study the structure and dynamics of spicules seen at the different filters. Individual spicules have been selected and intens...

We use time series of G-band and Ca II H filtergrams obtained by SOT on-board Hinode, as well as Halpha filtergrams in 5 wavelengths along the line profile obtained by the Dutch Open Telescope during a coordinated campaign. Our goal is to study the oscillatory behavior of a network region as seen at different heights of the solar atmosphere and to...

We have studied spicules observed at the northern solar limb by using simultaneous high resolution image sequences. The images were obtained by Hinode/SOT (in the Ca II H passband) and TRACE (in the 1600 Å passband) during a coordinated campaign. Both data sets were reduced and then carefully co-aligned in order to compare the observed patterns in...

High resolution optical spectra of chromospheric spicules obtained in the H? line are studied together with slit-jaw filtergrams. The spectra were recorded along a vertical slit parallel to the solar limb with the HSFA2 (Horizontal-Sonnen-Forschungs-Anlage) Solar Spectrograph at Ondrejov Observatory on August 19, 2007 and show H? line profiles take...

We present BVRI observations of two not previously studied eclipsing binary stars. A significant number of times of minima were determined and therefore new more accurate ephemerides were produced. Neither photometric elements nor spectral types for these two variable stars were known, thus a first approximation of their effective temperature and a...

One of the main features of the quiet solar chromosphere is the Network Bright Points (NBP), formed by emerging magnetic flux at the boundaries of supergranular cells. Using SSW IDL routines and wavelet analysis of series of images in four bandpasses (CaIIK 3, Mgb 1, Mgb 2 and Hα core) we have detected MHD wave modes in the Network Bright Points o...

It is the first time complete light curves have been acquired and a more thorough analysis has taken place for EA-type binaries FO Aur and V1025 Her. Our data set consists of four-color imaging (BVRI) obtained at NOA (Kryoneri, 1.2m telescope). The deduced light curves were acquired using GAIA Starlink software.

We present preliminary results of BVRI photometry of binary stars out of an observing list of short period binaries without any previous multifilter observations. The purpose of this project is to obtain photometric elements and the absolute parameters for further understanding of the evolutionary processes for these systems. The observations took...

One of the main features of the quiet solar chromosphere is the Network Bright Points (NBP), formed by the emerging magnetic flux, at the boundaries of supergranular cells. Triggered by the motions of magnetic loop foot‐points, at the top of the convection zone, MHD waves propagate inside the NBP’s. Using SSW IDL routines and wavelet analysis of s...

We present preliminary results of BVRI photometry of binary stars out of an observing list of short period binaries without any previous multifilter observations. The purpose of this project is to obtain photometric elements and the absolute parameters for further understanding of the evolutionary processes for these systems. The observations took...